The present invention relates to a process for producing a solventless silicone resin and more particularly the present invention relates to a solventless silicone resin and a process for producing a solventless silicone resin where such silicone resin has a viscosity varying anywhere from 200 to 5,000 centipoise at 25.degree. C.
Silicone resins are well known in the art. Such silicone resins usually comprise a resin compound of trifunctional siloxy units and difunctional siloxy units with a silanol content varying anywhere from 0.1 to 8% and optionally an alkoxy content varying anywhere from 0 to 4% by weight. Such silicone resins composed of trifunctional siloxy units and difunctional siloxy units are the most prevalent type of silicone resins for forming varnishes and silicone based paints, as well as for forming molding and encapsulating silicone compositions. It should be noted that such silicone resins are desired in the above applications since it has been found that products produced from silicones and silicone resins usually have better high temperature stability and weatherability properties as compared to traditional organic compositions.
There is also present in silicone chemistry, silicone resins composed of monofunctional siloxy units and tetrafunctional siloxy units with optionally difunctional siloxy units. However, such resins have been found to be more useful in the production of surfactants and silicone adhesives rather than in the fabrication of coatings. Accordingly, a highly successful silicone coating usually comprises one having trifunctional siloxy units and difunctional siloxy units since the combination of such units in a silicone resin give the resin, when it cures, the appropriate hardness while at the same time giving it some flexibility such that it can in some cases withstand extreme temperature cycling which is not possible with organic resins and compositions. An example of a suitable silicone resin to be found in the prior art is, for instance, that disclosed in the patent of Roedel, U.S. Pat. No. 3,846,358, whose disclosure is hereby incorporated by reference. This reference provides the production of a silicone resin without the use of a water immiscible organic solvent, but by the use of an aliphatic alcohol.
Simply the Roedel process comprises taking a mixture of alcohol and water in the appropriate amounts, adding it to the organochlorosilanes, and producing the appropriate alkoxylated siloxane. The alkoxylate is then washed with an aliphatic alcohol such that the acidity of the silicone alkoxylate is in the area of 1000 parts per million of acid or below. Then there is added an alkali metal hydroxide to the silicone hydrolyzate to further reduce the acidity to the desired level.
Finally, there is added to the silicone alkoxylate additional water and an aliphatic alcohol as a solubilizing agent to hydrolyze most of the alkoxy groups in the silicone alkoxylate to form the desired silicone resin therefrom. The alcohol is then stripped from the silicone resin to leave behind a solid mass or the resin may be cut in organic solvent for use in various products and compositions such as varnishes, silicone paints, molding compositions and also as a silicone resin encapsulant. However, while such silicone resins have many advantages they have one well-known disadvantage, they cannot be utilized as solventless resins in liquid form. Accordingly, in most cases, to utilize such silicone resins, it is necessary to utilize an organic solvent to dissolve the silicone resin so that it is present in anywhere from 5% to 90% silicone solids in solution so that it can be utilized and incorporated in various compositions.
It should be noted with respect to the Roedel process, in Column 6 beginning with line 42, Roedel points out that there is sufficient water added to his silicone resin such that most of the alkoxy and halogen groups are removed from his final silicone resin product. In addition, Roedel points out specifically in Column 7, line 32, that his silicone resin has an alkoxy content that varies from 0.2 to 4.0% by weight. Further, it should be noted that in Example 1, the silicone resin product that was obtained by the procedure of Roedel was a hard brittle solid. Accordingly, this disadvantage of the silicone resin of Roedel, that is in order for it to be a liquid at room temperature, it has to be dissolved in an organic solvent and is a disadvantage that has gained more prominence recently.
Accordingly, organic solvents while suitable for dissolving the silicone resin and preparing an appropriate solution have the disadvantage that they have to be disposed of or evaporated after the silicone resin has been incorporated into a composition. Accordingly, because of restrictions in many geographical areas much care and thought has to be allotted to the proper handling and disposal of such solvents after they have been utilized in the particular process.
Accordingly, the use of organic solvents results in unnecessary expense in whatever process they are utilized in, both in their initial cost and in their final disposal.
It should be noted that while the Roedel patent involved a process which did away with the use of hydrocarbon solvents in the actual process of producing the silicone resin, nevertheless, because of the form that the final product is produced a hydrocarbon solvent is needed for the final silicone resin product to be utilized properly.
Accordingly, for the above reasons, it was highly desirable to develop a solventless silicone resin system, that is, where the final silicone resin product would be a liquid of desirable low viscosity at room temperature, such that a solvent is not needed.
Solventless silicone resin system is, for instance, to be found in the patent of Mink, U.S. Pat. No. 3,948,848, which has recently issued. Such solventless silicone resins as disclosed in this patent comprise a two-component silicone resin system in which one-component comprises a vinyl-containing copolymer composed of trifunctional siloxy units and difunctional siloxy units, and the second component comprises a copolymer containing hydrosiloxy units in which the units themselves are selected from trifunctional siloxy units and difunctional siloxy units. In such compositions in either one or the other of the two components there is present a platinum catalyst. If it is desired to cure the composition of this patent the two compositions are mixed together and cured in the presence of a platinum catalyst to form a silicone encapsulating composition. It is also disclosed that such a composition can be utilized as a one-component system by the use of inhibitors. It is also disclosed that other less expensive catalysts may be used in such compositions by the patentee but nevertheless, it has been found by experience and as the patent states that platinum is the most preferred catalyst for such curing reactions.
While such composition has been found to be an appropriate encapsulating composition, it has several disadvantages. The most pronounced disadvantage is that it is quite expensive because of the use of two components and also the platinum catalyst. Further, such two component systems are difficult to work with by inexperienced applicators. Another disadvantage of such a composition as that disclosed in the foregoing Mink patent is that the cured composition does not have desirable thermal stability at temperatures above 250.degree. C. for extended periods of time. The reason for this is that the ethylene chain that is formed by the hydrogen atom adding on to the vinyl group in the curing of the silicone resin results in an ethylene bond which is not that stable at temperatures exceeding above 250.degree. C. Accordingly, both in terms of expense and in terms of properties, the above Mink composition while having many advantages has those disadvantages which detract from its utility.
Another development in the solventless systems is that to be found in Magne, U.S. Pat. No. 3,978,025. The Magne process has two disadvantages while it does produce a suitable solventless silicone resin system. In the Magne process, while the chlorosilanes are hydrolyzed in an alcohol-water mixture, nevertheless, in order to maintain a homogeneous medium Magne teaches the use of an organic solvent. Accordingly, his process has the disadvantage of the handling and disposal of such organic solvents.
Another disadvantage in Magne's process is that he discloses in Column 3 the use of a large excess of water in his final hydrolysis step.
Accordingly, it was highly desirable to develop a solventless silicone resin and a process for developing a solventless silicone resin having the appropriate low viscosities at room temperature, that is, a viscosity in the neighborhood of 200 to 5,000 centipoise at 25.degree. C., or preferably viscosities of 400 to 2,000 centipoise at 25.degree. C., which do not utilize a hydrocarbon solvent in the process for their production, and which are inexpensive to produce and use. Accordingly, it is one object of the present invention to provide for an improved process for producing solventless silicone resins without using hydrocarbon solvents.
It is an additional object of the present invention to provide for an improved solventless silicone resin system which is inexpensive and simple to produce.
It is an additional object of the present invention to provide for a solventless silicone resin system which has a viscosity varying anywhere from 200 to 5,000 centipoise at 25.degree. C.
It is still an additional object of the present invention to provide for a solventless silicone resin having a viscosity that does not exceed 5,000 centipoise at 25.degree. C. that is composed of trifunctional siloxy units and difunctional siloxy units having a silanol content that varies from 1 to 4% and having a methoxy content that varies from 7 to 14% by weight.
It is yet an additional object of the present invention to provide for a process for producing a solventless silicone resin system which is eminently suitable for the production of silicone paints and silicone varnishes. These and other objects of the present invention are accomplished by means of the disclosure set forth hereinbelow.